Since 1969, when McCord and Fridovich found that, from a biochemical function viewpoint, superoxide dismutase is an enzyme capable of scavenging active oxygen by catalyzing the reaction: 20.sub.2.+2H.sup.+ .fwdarw.H.sub.2 O.sub.2 +O.sub.2, a large number of studies have been made on the antiinflammatory, pigmentation preventing, autoxidation preventing and, furthermore, aging controlling and anticancer activities of superoxide dismutase.
Manganese-containing superoxide dismutase (hereinafter referred to as "Mn-SOD") has been discovered in eukaryotic cells and in animal and plant mitochondria. It is also known that this Mn-SOD occurs in the human epidermis [cf. e.g. Noritaka Ohkuma et al., Japanese Journal of Dermatology, 92 (5), 583 (1982); Kiyoshi Toda, The Journal of the Japanese Society for Cutaneous Health, No. 8, 38 (1982); Katsuhito Sugiura et al., Japanese Journal of Dermatology, 95 (14), 1535 (1985); N. Ohkuma et al., J. Dermatology, 14, 562 (1987)].
Studies have been conducted also on the production and isolation of Mn-SOD [cf. e.g. Japanese Kokai Tokkyo Koho (published unexamined patent application) 29285/1982; Japanese Patent Publication No. 48514/1988; Reddy, C. D. et al., Biochem. Int., 8 (5), 707 (1984)]. However, Mn-SOD has a drawback in that its enzyme activity decreases in aqueous systems, namely its stability is unsatisfactory.
For achieving an improvement in this respect, attempts have been made to chemically modify Mn-SOD to give modifications of manganese-containing superoxide dismutase (hereinafter referred to as "modified Mn-SOD") [cf. e.g. Japanese Kokai Tokkyo Koho No. 115280/1987; Kazuo Hayano, Kagaku to Kogyo (Chemistry and Industry), 39 (9), 678 (1986); Japanese Patent Publication No. 48514/1988; Koichi Miyata, Monthly Bio/Industry, 5 (7), 494 (1988)]. However, satisfactory results have not been obtained as yet.
Furthermore, several investigations have been carried out so far concerning the stabilization of Mn-SOD or modified Mn-SOD in cosmetic compositions [cf. e.g. Japanese Kokai Tokkyo Koho No. 87712/1980; Japanese Patent Publication No. 44800/1987; Japanese Kokai Tokkyo Koho No. 96107/1989; U.S. Pat. No. 4129644]. Under existing circumstances, however, satisfactory results have not been attained as yet in this respect.